This page describes an upcoming enhancement to TclOO: Property tracking. Please stay tuned.

The concept: Adding information that is tracked by class that allows the developer to embed data inside of classes

**New tools**

***Property subcommand***

    :   '''[info class] property''' ''class arguments'' 

This method allows access to this class. Arguments that follow are the same as allowed by the "dict" command.

   '''[info class] property''' ''class'' '''get''' ''field ?field...?'':   Return a value for a property, or die trying.
   '''[info class] property''' ''class'' '''getnull''' ''field ?field...?'':   Return a value for a property, or an empty list if the value does not exist.
   '''[info class] property''' ''class'' '''exists''' ''field ?field...?'':   Return true if a property exists
   '''[info class] property''' ''class'' '''list''' ''field ?field...?'':   Return a list of keys below the level ''field ?field...?''
   '''[info class] property''' ''class'' '''set''' ''field ?field...? value'':   Add/modify a property

There will be an equivalent lookup based on objects.

    :   '''[info object] property''' ''object''

This method provides objects access to the property database of their class. (Without the hassle of having to look up their class.) At present, it is read only.

   '''[info object] property''' ''object'' '''get''' ''field ?field...?'':   Return a value for a property, or die trying.

   '''[info object] property''' ''object'' '''getnull''' ''field ?field...?'':   Return a value for a property, or an empty list if the value does not exist.

   '''[info object] property''' ''object'' '''exists''' ''field ?field...?'':   Return true if a property exists

   '''[info object] property''' ''object'' '''list''' ''field ?field...?'':   Return a list of keys below the level ''field ?field...?''

**New Keywords**

The following keywords will be added to [oo::define]:

    :   '''property''' ''field ?field...? value''

Set a property from the class definition.

**Usage**

This system was originally intended to provide a Tk option-like database for TclOO objects. 
======
    # Dump the entire option dictionary
    set option_dict [info object [self] property get option]

    # Access a list of options
   set option_list [info object [self] property list option]

    # Check if an option exists
   set exists [info object [self] property exists option color]

    # Get the default value for color
   set color [info object [self] property getnull option color default]

  oo::define oo::class_withopts {
     constructor args {
        my InitializePublic {*}$args
     }

    method InitializePublic args {
        my variable config
        set optiondict [info object [self] property get option]
        # Populate config() with defaults
        foreach {field info} $optiondict {
          if {[info exists config($field)]} continue
          if {[dict exists $optiondict $field]} {
            set config($field) [dict get $optiondict default]
           } else {
             set config($field) {}
           }
        }
        foreach {field value} $args {
          set key [string trimleft $key -]
          if {![dict exists $optiondict $key]} {
             error "Bad option: $key, valid: [lsort -dictionary [dict keys $optiondict]]"
          }
          set config($field) $value
        }
     }

     method configure args {
        my variable config
        set triggers {}
        set optiondict [info object [self] property get option]
        foreach {key value} $args {
          set key [string trimleft $key -]
          if {![dict exists $optiondict $key]} {
             error "Bad option: $key, valid: [lsort -dictionary [dict keys $optiondict]]"
          }
        }
        foreach {key value} $args {
          set key [string trimleft $key -]
          if {$value != $config($key)} {
             set config($key) $value
             if {[dict exists $optiondict $field trigger]} {
               lappend triggers $field $value [dict get  $optiondict $field set-script]
             }
          }
        }
        foreach {field value script] $triggers {
           eval [string map [list %object% [self] %self% [self] %field% $field %value% $value] $script] 
        }
     }

    method cget field {
       set field [string trimleft $field -]
       if {![info object property [self] exists option $field]} {
          error "Invalid option $field, Valid [info option property [self] list option]"
       }
       my variable config
       return $config($field)
    }
  }
======
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